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Layer 1: Physical Layer Network Media

Layer 1: Physical Layer Network Media. Review. What did we do last week? Reference Models and Standards OSI – 7 Layer Model TCP/IP Model Essential building blocks of Computer Communications Sender/Receiver Message Rules Confirmation. Review - Information Transfer. Transmission Media.

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Layer 1: Physical Layer Network Media

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  1. Layer 1: Physical Layer Network Media RD-CSY1017

  2. Review • What did we do last week? • Reference Models and Standards • OSI – 7 Layer Model • TCP/IP Model • Essential building blocks of Computer Communications • Sender/Receiver • Message • Rules • Confirmation RD-CSY1017

  3. Review - Information Transfer Transmission Media Message Encoder Transmitter Message Decoder Receiver • Communication begins with a message, or information • Message are sent across a data network by breaking into small chunks called packets. • Communication uses a medium to transfer information. • Which layer of OSI model it refers to? RD-CSY1017

  4. Physical Layer • Objectives • Introduction to different cable types. • Unshielded twisted-pair cable (UTP). • straight-through, • crossover, and • rollover cables • Fiber-optic cable • Wireless RD-CSY1017

  5. Physical Layer • The essential service provided by the physical layer consists of an unstructured bit stream, which can be used by higher layers to provide the basis for higher layer communication services

  6. Physical Layer- data Signals • Signals on the physical media are influenced by noise

  7. Physical Layer • Physical layer is guided Media and Unguided Media

  8. Guided Media Types Copper Glass Twisted Pair Coaxial Cable Fibre Optic Unshielded Twisted Pair Shielded Twisted Pair Screened Twisted Pair Mono mode Multi mode Physical Media Types Physical Media Unguided Media ( Wireless) Twisted Pair cable Fibre optic cable Coaxial cable RD-CSY1017

  9. Factors guiding choice of media • Distance over which signal can be transported without being amplified due to signal distortion and attenuation • Speed at which data transfer would happen • Cost of media • Construction and installation • Heavy, flexible and installation RD-CSY1017

  10. Speed of Data Transfer: Bandwidth • Data rate • transferring data per unit of time. • Data rate determines how long it will take to transfer a file. • The larger the file, the longer it takes, as there is more information to transfer. • What is the basic unit of data/data transfer? • Bit/bits per second RD-CSY1017

  11. Bandwidth (BW)– Rate of Information Transfer • Bandwidth is the amount of information that can flow through a network connection in a given period of time. • Analogy (road traffic): Wider the road, more the number of lanes possible and more the number of cars, it can handle • Measured in bits per second (bps). • e.g. 100 Kilo bits per second or 100Kbps • Faster data rate =>quicker information travel • Which units are more commonly used than others ? RD-CSY1017

  12. Internet ISP Connectivity • Roughly hierarchical • Divided into tiers • Tier-1 ISPs are also called backbone providers, e.g., AT&T, Verizon, Sprint, Level 3, Qwest • An ISP runs (private) • Points of Presence (PoP) where its customers and other ISPs connect to it • ISPs also connect at (public) Internet Exchange Point (IXP) • public peering http://en.wikipedia.org/wiki/List_of_Internet_exchange_points_by_size

  13. Wide Area Cable Network • Fiber node: 500 - 1K homes • Distribution hub: 20K - 40 K homes • Regional headend: 200 K - 400 K homes

  14. Wide Area Access using telephone cable: ADSL • Asymmetrical Digital Subscriber Loop (ADSL) • Telephone company’s solution to “last mile problem”

  15. Light is used to carry data using light / no light or increasing/decreasing light intensity Electronic circuits are used to convert light back to data Fibre Optic Cabling RD-CSY1017

  16. Fiber Media • Light travels through the optical media by the way of total internal reflection. • Modulation scheme used is intensity modulation. • Two types of Fiber media : • Multimode • Many pulses of light generated by LED travel at different angles • Single mode • Carries light pulses along single path • Uses Laser Light Source • Multimode Fiber can support less bandwidth than Singlemode Fiber. • Singlemode Fiber has a very small core and carry only one beam of light. It can support Gbps data rates over > 100 Km without using repeaters.

  17. FTTP (Fiber to the Premises ) • Highest theoretical capacity per user: 1 Gbps • currently 5 to 30 Mbps downstream, 2 to 5 Mbps upstream • Services • analog and digital video • video viewable with and without set-top converter • voice • interfaces with existing phone, data, video cabling

  18. FTTP Architecture: Fiber Distribution Terminal (FDT)

  19. Copper Media: Twisted Pair • Twisted-pair is a type of cabling that is used for most modern Ethernet networks. • A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs.There are two basic types, • shielded twisted-pair STP) • unshielded twisted-pair (UTP).

  20. Unshielded twisted-pair Consists of four pairs of colour-coded wires that have been twisted together and then encased in a flexible plastic sheath. Used for Local Area Networks (LAN) IEEE is the standards body that classifies data cables according to their bandwidth e.g., Category 5 (Cat5) cable Other categories include Enhanced Category 5 (Cat5e) cable and Category 6 (Cat6), Category 6e (Cat6) Computer data cables:Unshielded Twisted Pair (UTP) RD-CSY1017

  21. Shielded twisted-pair cable (STP) • Shielded twisted-pair cable (STP) combines the techniques of shielding, cancellation, and twisting of wires. • Each pair of wires is wrapped in metallic foil. • The four pairs of wires are wrapped in an overall metallic braid or foil. RD-CSY1017

  22. UTP Cable Specifications • Cat 3 UTP • Category 3 UTP is rated to carry data up to 10Mbit/s • Cat 5 UTP • Category 5 UTP is rated to carry Ethernet up to 100Mbit/s and ATM up to 155Mbit/s • Cat 5e UTP • Category 5e UTP is an enhanced version of Cat 5 UTP. • Rated to carry data up to 1000Mbit/s. • Standard cable for use with Ethernet 1000Base-T. • Can also be used to extend the distance of 100Base-TX cable runs up to 350 meters. • Cat 6 and 7 UTP • Emerging standards rated for 250 and 600 MHz respectively RD-CSY1017

  23. Wireless Networks : General Characteristics • No physical wire • Differences from wired link …. • decreased signal strength: radio signal attenuates as it propagates through matter (path loss) • interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere • multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “difficult” RD-CSY1017

  24. Comparing the cables RD-CSY1017

  25. Your Turn • Five new things you have learnt in this session: • ? • ? • ? • ? • ? RD-CSY1017

  26. Next Week.. • Layer 2- Data Link Layer • Media Access Protocols • Ethernet • Token Ring • FDDI • Layer 2 Devices RD-CSY1017

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